Pressure relief valve with auxiliary loading device

ABSTRACT

A pressure relief valve including a valve member movable between open and closed positions to control fluid flow. A body member is provided which receives a piston operatively connected to the valve member for operating same. The piston defines a first chamber in the valve body extending above the piston and a second chamber extending below the piston. System fluid is introduced into the chambers and the differential fluid pressure in the chambers applies a loading force to the piston, and therefore to the valve member in its closed position. When the system pressure, and therefore the pressure in the chambers, exceeds a predetermined amount the pressure in one of the chambers is vented, causing the piston to move to an open position and permit opening movement of the valve member.

This is a continuation of copending application Ser. No. 07/843,853filed on Feb. 27, 1992, now U.S. Pat. No. 5,234,023.

BACKGROUND OF THE INVENTION

This invention relates to a pressure relief valve and, moreparticularly, to a pressure relief valve in which an additional loadingforce is applied to its valve member.

Pressure responsive relief valves are used in many applications toprevent operating systems utilizing pressurized fluid from reachingdangerously high pressures. Such valves usually include a nozzle havinga valve seat which is normally closed by a valve member slidablydisposed in the body of the valve. The valve member typically is biasedto a closed position against the valve seat by a compression spring, orthe like. When the system pressure exceeds a predetermined set value,the valve member opens and places the nozzle passage in fluidcommunication with an exhaust port in the valve body. When the pressurein the nozzle passage then decreases by a specified incremental amountto arrive at the reseating pressure for the valve, the valve member isagain forced into a seated position on the valve seat under the actionof the compression spring to close the valve.

In these types of arrangements, the valve member must seat very tightlyon the valve seat to prevent leakage, particularly at pressuresapproaching the set pressure of the valve, and several techniques haveevolved to improve seat tightness. For example, the valve members areprovided with a highly machined replaceable disc formed of stainlesssteel, or like material, which engages a highly machined contactingsurface of the valve seat. Also, the valve seats are machined torelatively narrow widths which offer a small contact area with the discmember.

Another technique for achieving even greater seat tightness involves theuse of a so-called "soft seat" valve configuration in which a resilientO-ring, or the like, is secured to the valve member so that contactbetween the outer edge of the valve seat and the O-ring provides asealing function. However, these soft seat valves are not as durable asvalves provided with the machined metal surfaces.

Still other techniques for improving seat tightness involve additionalloading to the valve member utilizing external energy. However, thesetechniques are often complicated, not fail safe and add to the cost ofthe system.

Therefore, it is still a goal of designers to provide pressure reliefvalves with increased seal tightness, decreased fluid leakage, andincreased durability without attendant increases in complexity and cost.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a pressure reliefvalve for controlling fluid flow in which additional loading is placedon the valve to increase seat tightness and reduce fluid leakage.

It is a further object of the present invention to provide a pressurerelief valve of the above type in which the additional loading isachieved utilizing the pressure of the fluid.

It is a further object of the present invention to provide a pressurerelief valve of the above type which responds quickly and reliably to apredetermined fluid pressure for releasing the additional loading topermit the valve to open.

It is a still further object of the present invention to provide apressure relief valve of the above type which does not expend anyexternal energy.

It is a still further object of the present invention to provide apressure relief valve of the above type which is durable.

Toward the fulfillment of these and other objects, the pressure reliefvalve of the present invention comprises a valve member movable betweenopen and closed positions to control fluid flow in a system. A piston isoperatively connected to the valve member and defines -a first chamberin the valve body extending above the piston and registering with aninlet in the valve body, and a second chamber extending below the pistonand registering with another inlet. The system fluid is introducedthrough the inlets and into the chambers and the differential fluidpressure force in the chambers creates a loading force on the piston,and therefore on the valve member. When the system pressure, andtherefore the pressure in the chambers, exceeds a predetermined amount,the pressure in one of the chambers is vented, causing the piston tomove to an open position.

BRIEF DESCRIPTION OF THE DRAWINGS

The above brief description, as well as further objects, features andadvantages of the present invention will be more fully appreciated byreference to the following detailed description of the presentlypreferred but nonetheless illustrative embodiments in accordance withthe present invention when taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a cross-sectional view depicting the pressure relief valve ofthe present invention shown in a closed position;

FIG. 2 is a view similar to FIG. 1 but depicting the valve of FIG. 1 inan open position; and

FIG. 3 is a partial cross-sectional view of an alternate embodiment ofthe pressure relief valve of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2 of the drawings, the reference numeral 10refers in general to a pressure relief valve which includes a basemember 12 and a bonnet member 14 secured to the base member by aplurality of bolts 16 extending through aligned openings in the members12 and 14 and receiving a plurality of nuts 18. The base member 12 isprovided with an inlet nozzle 20 which is connected to a source of fluidwhose flow is to be controlled, and an exhaust port 22 through which thefluid is expelled when the valve 10 is in its open position. The nozzle20 defines an internal bore, or passage 20a which terminates in anenlarged opening to define a valve seat 26 (FIG. 2). The base member 12and the bonnet member 14 define an internal chamber which receives avalve unit 28 which is mounted for reciprocal movement in the chamber.The valve member 28 includes a disc holder 30 which is slidably disposedwithin a guide sleeve 32 coaxially mounted in the base member 12 by atransverse mounting plate 34 secured between the base member 12 and thebonnet member 14. The disc holder 30 supports a disc 36 having amachined face 36a (FIG. 2) which, in the closed position of the valvemember 28 shown in FIG. 1, rests upon the valve seat 26. The disc holder30 is provided with an annular skirt 30a which projects downwardly fromthe disc holder and defines with an adjustment ring 38 threadedlyengaged to the outer surface of the nozzle 20, an adjustment orifice forregulating the blowdown, or reseating, pressure of the valve as will bedescribed.

The valve unit 28 also includes a spindle 40 provided at its lower endwith an enlarged head 40a the lower portion of which is seated in acorresponding recess at the upper end of the disc holder 30 and isretained therein by means of a split retaining ring 42. A washer 44extends over the lower end portion of spindle 40 and rests upon theshoulder defined by the head 40a. A washer 46 extends over the upper endportion of the spindle and is limited in upward movement by the bottomshoulder of an adjusting screw 48 which is threaded within a top plate14a of the bonnet member 14.

A compression spring 50 extends over the spindle 40 and is interposedbetween the washers 44 and 46. The compressive force exerted by thespring 50 can be adjusted by moving the adjustment screw 48, andtherefore the washer 46, up or down as viewed in the drawings. A nut 51engages the upper end of the screw 48 to retain the screw at a desiredposition corresponding to the amount of compressive force exerted by thespring 50.

An eductor tube 52 is provided within the interior of the base member 12and has one end secured in an opening in the transverse plate 34 and theother end extending into the exhaust port 22. The eductor tube 52 thuscommunicates with the interior of the bonnet member 14 and functions toremove fluid that leaks into the interior of the bonnet member by asyphon effect created by the fluid flow through the port 22. The abovecomponents of the pressure relief valve 10, along with further details,are fully disclosed in U.S. Pat. No. 4,858,642 assigned to the assigneeof the present invention, the disclosure of which is incorporated byreference.

A housing 56 is mounted over the upper portion of the bonnet member 14and is connected to, and in threaded engagement with, a circular flange14b extending from the top plate 14a of the bonnet member 14. The lowerportion of the housing 56 receives the upper end portion of the spindle40, and a horizontal partition 56a extends across the interior of thehousing 56 to define an operating chamber 58 in the upper portion of thehousing which receives a piston 60. A stem 62 extends from the lowersurface of the piston 60 and through an opening extending through thepartition 56a, and its lower end abutts the upper end of the spindle 40.The stem 62 includes an enlarged portion 62a which, before the housing56 is mounted to the plate 14a, rests on the upper surface of thepartition 56a. An O-ring 64 is disposed in a corresponding grooveprovided in the wall of the partition 56a defining the opening in thepartition to seal against fluid leakage from the chamber 58.

Two inlet conduits 68a and 68b extend through corresponding openings inthe housing 56 and register with the chamber 58. It is understood thatthe conduits 68a and 68b are connected to the same source of fluid thatis being controlled by the pressure relief valve 10, i.e. the samesource that is connected to the inlet of the nozzle 20.

In the closed position of the valve unit 28 shown FIG. 1, the piston 60is positioned between the inlet conduits 68a and 68b so that the chamber58 is divided into an upper portion 58a extending above the piston 60and a lower portion 58b extending below the piston. A spring 70 isprovided in a bore formed in the upper chamber portion 58a and extendsbetween the piston 60 and a plug 72 in threaded engagement with theupper end portion of the latter bore. This bore is stepped to define ashoulder 56b against which the upper surface of the piston 60 abuttswhen the piston is in its open position of FIG. 2, as will be furtherdescribed. The axial position of the plug 72 in the bore can thus bevaried to vary the force exerted by the spring 70 on the piston 60. Theplug 72 is provided with an outlet passage 72a over which a dead weightvent cap 74 extends to vent the upper chamber portion 58a underpredetermined conditions that will be described.

The piston 60 is adapted for reciprocal movement within the chamber 58and an O-ring 76 extends in a circular groove formed in the outercircumference of the piston which engages the corresponding inner wallof the body member 56 to prevent fluid leakage between the chamberportions 58a and 58b. The upper surface of the piston 60 exposed to thefluid in the chamber portion 58 is greater than the lower surface of thepiston exposed to the pressure in the lower chamber portion 58b due tothe presence of the valve stem 62. Thus, the downward force exerted onthe piston 60 by the fluid in the chamber portion 58a is greater thanthe upward force exerted on the piston by the fluid in the chamberportion 58b, with the spring 70 providing some additional downward forceagainst the piston 60. Thus, the piston 60 is normally forced to itsclosed position in the lower portion of the chamber 58 as shown in FIG.1 by the action of the force exerted by the fluid pressure in the upperchamber portion 58a in excess of that exerted by the fluid pressure inthe lower chamber portion 58b and by the action of the spring 70.

In operation, the nozzle 20, as well as the inlet conduits 68a and 68b,are connected to the source of fluid to be controlled. The vent cap 74is selected and the spring 50 is adjusted by rotation of the screw 48 sothat the vent cap and the valve member 28 respond to a predeterminedpressure of the system fluid. Assuming that the latter fluid pressuredoes not exceed the predetermined value, the spring 50 acts against thevalve member 28 to force it to its closed position in the sealingrelationship with the valve seat 26 shown in FIG. 1, thus preventing theflow of the fluid through the nozzle 20, the interior of the base member12 and out the exhaust port 22. Also, the piston 60 is forced to itslower, closed position of FIG. 1 by the differential fluid pressure inthe upper chamber portion 58a and the lower chamber portion 58b, alongwith the force of the spring 70. Thus the piston 60, and therefore thestem 62, act against spindle 40 to provide an additionaldownwardly-directed loading force to the valve member 28 to maintain itin its closed position of FIG. 1 and to provide an increased loading onthe seal between the machined face 36a of the disc 36 and the valve seat26.

When the pressure of the system fluid exceeds the predetermined value,causing a corresponding increase in the fluid pressure in the chamberportion 58a, the vent cap 74 opens to relieve the fluid pressure in theupper chamber portion 58a. The design is such that the above-mentionedpredetermined pressure creates an upward force applied to the piston 60by the fluid in the lower chamber portion 58b which force is greaterthan the downward force applied by the spring 70. Therefore, thedownward force exerted on the spindle 40 by the piston 60, via the stem62, is eliminated and the piston is forced upwardly to the positionshown in FIG. 2 in which it abutts the shoulder 56b. This predeterminedpressure of the system fluid also applies an upward force against thevalve unit 28 which exceeds that of the compression spring 50, and thevalve unit 28 moves to its open position shown in FIG. 2. In thisposition the system fluid is permitted to flow through the nozzle 20,the interior of the base member 12 and exit through the exhaust port 22.

It is noted that, in the open position of FIG. 2, the piston 60 ispositioned above the inlet conduit 68a and the corresponding opening inthe body member 56, thus shutting off the fluid flow into the upperchamber portion 58a. Therefore, this eliminates the unnecessary flow ofthe high pressure fluid through the chamber portion 58a and the openvent cap 74.

The valve unit 28 will stay in its open position of FIG. 2 until thefluid pressure drops down to a predetermined reseat pressure causingmovement of the spindle 40 and movement of the valve member 28downwardly to the closed position of FIG. 1 under the action of theforce provided by the spring 50. Also, since the force exerted on thepiston 60 by the spring 70 can be adjusted by rotating the plug 72 sothat this reseat pressure reduces the force in the lower chamber portion58b to a value which is less than the force applied to the piston 60 bythe spring 70 and pressure in the upper chamber portion 58a, the pistonmoves back towards the position of FIG. 1 under the force of the spring.This permits the system fluid to enter the upper chamber portion 58athrough the inlet conduit 68a which fluid, together with the force ofthe spring 70, again applies the additional downward loading force tothe valve unit 28, via the stem 62 and the spindle 40.

The adjustment ring 38 can be rotated to adjust its axial position onthe nozzle 20 to regulate the size of the adjustment orifice definedbetween the skirt 30a of the disc holder 30 and the ring 38, to regulatethe reseat pressure of the valve, as described in the above-referencedpatent.

It is thus seen that the pressure relief valve of the present inventionapplies an additional seat-engaging, loading force to the valve member28 to provide a very high degree of seat tightness. Also, the valve ofthe present invention responds quickly and reliably to the existence ofthe predetermined threshold system fluid pressure for instantlyrelieving the force and permitting opening of the valve member. Further,the valve of the present invention is relatively simple in structure andoperation-and utilizes the system fluid instead of external energy.

FIG. 3 depicts an alternate embodiment of the pressure relief valve ofthe present invention in which the vent cap 74 is replaced by anadjustable, spring-loaded valve. More particularly, anexternally-threaded circular flange 72a is provided on the plug member72 of the previous embodiment and a sub-housing 80 is mounted over theplug member 72 with its lower end position in threaded engagement withthe flange 72a. A valve member 82 is located in the sub-housing 80 andis normally forced by a spring 84 into engagement with a seat defined bythe upper surface of the flange 72a to block the upper end of the outletpassage 72a. The spring 84 extends between the valve member 82 and thehead of a bolt member 86 which is in threaded engagement with an openingformed through the upper end of the sub-housing 80. Thus, the axialposition of the bolt member 86 can be adjusted to vary the force exertedon the valve member 82 by the spring 84. An opening 80a extends throughthe wall of the sub-housing 80 to provide a outlet for the fluid ventingfrom its chamber 58a.

The force exerted on the valve member 82 by the spring 84 can be set sothat, when the pressure of the system fluid exceeds the above-mentionedpredetermined value causing a corresponding increase in the fluidpressure in the upper chamber portion 58a, the valve member 82 opensagainst the force of the spring 84. This enables the high pressure fluidto pass from the chamber 58a, through the passage 72a and the interiorof the sub-housing 80 and discharge through the outlet opening 80a.Otherwise, the structure, operation and advantages of the embodiment ofFIG. 3 are identical to those of FIGS. 1 and 2.

It is understood that other variations may be made in the foregoingwithout departing from the scope of the invention. For example, the stem62 of the piston 60 can be attached to the spindle 40 in which case thedevice of the present invention would also provide a pulling force onthe valve member 28 under the conditions described above to assist thedisc 36 to open.

Still other variations, modifications, changes and substitutions areintended in the foregoing disclosure and in some instances some featuresof the invention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theinvention.

What is claimed is:
 1. A pressure relief valve assembly comprising:meansdefining a first chamber having an inlet for receiving fluid from anexternal source and an outlet for discharging said fluid; a valve membermovable between an open and closed position in said chamber and in thepath of said fluid flow between said inlet and said outlet so that saidfluid urges said valve member to one of said positions; a stem extendingfrom said valve member; means including a spring engaging said stem fornormally biasing said valve member to the other of said positions sothat said valve member moves to said one position in response to thefluid pressure exceeding a predetermined value; means defining a secondchamber in a spaced relation to, and isolated from, said first chamberfor receiving fluid from said source and for discharging said fluid;piston means disposed in said second chamber and responsive to a fluidpressure in said second chamber for engaging said stem for applying anadditional force to said stem to force it, and therefore said valvemember, to said other position; a spring disposed in said second chamberand urging said piston towards said stem; and means responsive to saidpredetermined pressure for releasing the fluid pressure in said secondchamber to release said additional force and permit said valve member tomove to said one position.
 2. The assembly of claim 1 wherein saidadditional force is released by venting said second chamber in responseto said predetermined pressure.
 3. The assembly of claim 1 furthercomprising means responsive to the release of said additional force forshutting off the flow of said fluid into said second chamber.
 4. Theassembly of claim 1 wherein said one position is an open position andwherein said other position is a closed position.
 5. The assembly ofclaim 1 wherein said piston defines with said second chamber, a chamberportion extending above said piston for receiving fluid and a chamberportion extending below said piston for receiving fluid, the fluidpressures in said chamber portions creating oppositely-directed forceson the respective ends of said piston.
 6. The assembly of claim 5wherein the force applied to said piston by fluid pressure in one ofsaid chamber portions is greater than the force applied to said pistonby the fluid pressure in the other chamber portion to move said pistonto said stem-engaging position.
 7. The assembly of claim 6 wherein thearea of one end of said piston exposed to said fluid in said one chamberportion is greater than the area of said piston exposed to said fluid insaid other chamber portion to create said greater force.
 8. A pressurerelief valve assembly comprising:means defining a first chamber havingan inlet for receiving fluid from an external source and an outlet fordischarging said fluid; a valve member movable between an open andclosed position in said chamber and in the path of said fluid flowbetween said inlet and said outlet so that said fluid urges said valvemember to one of said positions; a stem extending from said valvemember; means including a spring engaging said stem for normally biasingsaid valve member to the other of said positions so that said valvemember moves to said one position in response to the fluid pressureexceeding a predetermined value; means defining a second chamber in aspaced relation to, and isolated from, said first chamber for receivingfluid from said source and for discharging said fluid; piston meansdisposed in said second chamber and responsive to a fluid pressure insaid second chamber for engaging said stem for applying an additionalforce to said stem to force it, and therefore said valve member, to saidother position; means responsive to said predetermined pressure forreleasing the fluid pressure in said second chamber to release saidadditional force and permit said valve member to move to said oneposition; and means responsive to the release of said additional forcefor shutting off the flow of said fluid into said second chamber.
 9. Theassembly of claim 8 wherein said additional force is released by ventingsaid second chamber in response to said predetermined pressure.
 10. Theassembly of claim 8 wherein said one position is an open position andwherein said other position is a closed position.
 11. The assembly ofclaim 8 wherein said piston defines with said second chamber, a chamberportion extending above said piston for receiving fluid, and a chamberportion extending below said piston for receiving fluid, the fluidpressures in said chamber portions creating oppositely-directed forceson the respective ends of said piston.
 12. The assembly of claim 8wherein the force applied to said piston by fluid pressure in one ofsaid chamber portions is greater than the force applied to said pistonby the fluid pressure in the other chamber portion to move said pistonto said stem-engaging position.
 13. The assembly of claim 12 wherein thearea of one end of said piston exposed to said fluid in said one chamberportion is greater than the area of said piston exposed to said fluid insaid other chamber portion to create said greater force.